U.S. patent number 6,111,630 [Application Number 09/127,959] was granted by the patent office on 2000-08-29 for liquid crystal projector having a cooler and an air velocity sensor.
This patent grant is currently assigned to Hitachi, Ltd., Hitachi Video and Information Systems, Inc.. Invention is credited to Sousuke Hisamatsu, Mitsugi Kojima, Kiyoshi Watanuki, Kouichi Yamamoto.
United States Patent |
6,111,630 |
Watanuki , et al. |
August 29, 2000 |
Liquid crystal projector having a cooler and an air velocity
sensor
Abstract
A liquid crystal projector, comprising: a liquid crystal panel;
a light source for irradiating light onto an image formed on the a
liquid crystal panel; a projection lens for enlarging and
projecting the image projected from the liquid crystal panel; a
cooler, such as a suction fan, for sending cooling air flow onto a
panel surface of the liquid crystal panel; an air velocity sensor
for sensing air velocity of the cooling air flow sent onto the
liquid crystal panel; and a protection device for protecting the
liquid crystal panel on a basis of a detected value of the air
velocity measured by the air velocity sensor. The is further formed
an air passage for passing the cooling air flow along with the
panel surface of the liquid crystal panel, and the air velocity
sensor is positioned in an exit portion of the cooling air flow
passing through the liquid crystal panel.
Inventors: |
Watanuki; Kiyoshi (Yokohama,
JP), Kojima; Mitsugi (Yokohama, JP),
Hisamatsu; Sousuke (Yokohama, JP), Yamamoto;
Kouichi (Yokohama, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
Hitachi Video and Information Systems, Inc. (Kanagawa-ken,
JP)
|
Family
ID: |
16993417 |
Appl.
No.: |
09/127,959 |
Filed: |
August 3, 1998 |
Foreign Application Priority Data
|
|
|
|
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Sep 1, 1997 [JP] |
|
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9-235935 |
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Current U.S.
Class: |
349/161; 348/748;
348/E5.141; 348/E5.143; 353/52; 353/57 |
Current CPC
Class: |
G02F
1/133385 (20130101); H04N 9/3141 (20130101); H04N
5/7441 (20130101) |
Current International
Class: |
G02F
1/13 (20060101); G02F 1/133 (20060101); H04N
5/74 (20060101); G02F 001/1333 (); H04N 005/74 ();
G03B 021/16 (); G03B 021/18 () |
Field of
Search: |
;349/161 ;353/52,57,61
;348/748 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
IBM Technical Disclosure Bulletin, vol. 29, No. 9, Feb. 1987, pp.
3930-3931, "Cooling Projection System for Passive Display", Feb.
1997..
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Primary Examiner: Malinowski; Walter
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Claims
What is claimed is:
1. A liquid crystal projector, comprising:
a liquid crystal panel;
a light source for irradiating light onto an image formed on said
liquid crystal panel;
a projection lens for enlarging and projecting the image projected
from said liquid crystal panel;
a cooler for providing cooling air flow onto a panel surface of
said liquid crystal panel;
an air velocity sensor for sensing air velocity of the cooling air
flow sent onto said liquid crystal panel; and
a protection device for protecting said liquid crystal panel on a
basis of a detected value of the air velocity measured by said air
velocity sensor, wherein there is further formed an air passage for
passing the cooling air flow along with the panel surface of said
liquid crystal panel, and said air velocity sensor is positioned in
an exit portion of the cooling air flow passing through said liquid
crystal panel.
2. A liquid crystal projector as defined in claim 1, wherein said
air velocity sensor comprises a heat generating body, a temperature
sensing element which changes electric characteristics thereof in
response to a surrounding temperature, and a temperature sensor for
measuring a temperature of the cooling air, whereby said air
velocity sensor detecting the air velocity of the cooling air flow
on basis of the change in the electric characteristics of said
temperature sensing element and compensating the detected value by
the temperature of the cooling air flow which is detected by said
temperature sensor.
3. A liquid crystal projector as defined in claim 2, wherein said
liquid crystal panel comprises three liquid crystal panels for
three colors of red, green and blue, which are positioned opposing
to three surfaces of a prism of a cubic shape, respectively, and
said air velocity sensor is positioned between said liquid crystal
panel and said prism.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal projector, in
particular, to that in which is applied to a technology for
protecting a liquid crystal panel from an increase in the
temperature thereof.
2. Description of Prior Art
Conventionally, it is common that a liquid crystal projector is
heated by light irradiated for projecting an image of a liquid
crystal panel, thereby increasing the temperature thereof. For
suppressing the increase in the temperature, cooling air is sent
onto the liquid crystal panel by means of a fan. Thereby,
generation of deformation in the liquid crystal panel, etc., due to
the increase of the temperature is prevented.
Such protection technology of the liquid crystal panel is already
disclosed and known by, for example, Japanese Patent Laying-Open
No. Hei 4-60533 (1992) and Japanese Patent Laying-Open No. Hei
4-60534 (1992). In Japanese Patent Laying-Open No. Hei 4-60533, it
is constructed by comprising a detection means of surrounding
temperature which is positioned in the vicinity of the liquid
crystal panel, a wind velocity detection means (or sensor) for
detecting wind velocity of the cooling air at an incident side with
respect to the liquid crystal panel, and a means for detecting the
lamp energy of a light source. An output of the surrounding
temperature detection means is sent a micro-computer, thereby if
the output which is sent to is higher than a preset upper limit
value, then it turns OFF an electric power source, and if it is
lower than that an information is sent to a control circuit. Also,
the output of the wind velocity detection means is sent to the
micro-computer, thereby if the wind velocity is less than a preset
value due to clog in a filter, etc., then it turns OFF the electric
power source, and if it is greater than the preset value, an
information is sent to the control circuit. Furthermore, an output
of the means for detecting the lamp energy is also sent to the
micro-computer, thereby if the energy is less than a preset value,
it indicates an exchange of the lamp, and if it is greater than the
preset value, an information is sent to the control circuit. On a
basis of the information of the surrounding temperature of the
panel, of the wind velocity at the incident side, and of the lamp
energy, which are sent to the control circuit, the revolution
numbers of a suction fan and an exhaustion fan are controlled so
that the temperature of the liquid crystal panel is less than a
predetermined constant value.
With the conventional art mentioned in the above, the wind velocity
sensor is positioned at a downstream side of an air flow of the
cooling air passing through the liquid crystal panel and the
exhaustion fan is positioned at a rear side of the liquid crystal
panel, therefore causing following problems. For instance, if the
clog or the like is caused in a suction system including the
suction fan due to any reason, the cooling air by the suction fan
is reduced down in the amount of wind as well as in the velocity
thereof, however, due to an affect of the air flow formed by the
exhaustion fan, the wind velocity which is detected by the wind
velocity sensor will not decrease down greatly, therefore it is
likely to fail to detect the decrease in the wind amount by the
suction fan so that the temperature of the liquid crystal panel
rises up.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, for overcoming
the problems in the above-mentioned conventional art, to provide a
liquid crystal projector equipped with a technology for suppressing
the increase of the temperature in the liquid crystal panel.
For achieving the above-mentioned object, in accordance with the
present invention, there is provided a liquid crystal projector,
comprising:
a liquid crystal panel;
a light source for irradiating light onto an image formed on said a
liquid crystal panel;
a projection lens for enlarging and projecting the image projected
from said liquid crystal panel;
cooling means for sending cooling air flow onto a panel surface of
said liquid crystal panel;
a wind velocity sensor for sensing wind velocity of the cooling air
flow sent onto said liquid crystal panel; and
a protection device for protecting said liquid crystal panel on a
basis of a detected value of the wind velocity measured by said
wind velocity sensor, wherein there is further formed an air
passage for passing the cooling air flow along with the panel
surface of said liquid crystal panel, and said wind velocity sensor
is positioned in an exit portion of the cooling air flow passing
through said liquid crystal panel.
With provision of said wind velocity sensor positioned in the exit
portion of the cooling air flow, it is possible to measure the
amount of the air supplied to the liquid crystal panel from said
cooling means suitably without the affect of said exhaust fan, etc.
Therefore, even in a case that the amount of the cooling air flow
supplied from said cooling is reduced due to the clog and the like,
it is possible to protect the liquid crystal panel appropriately.
In this case, it is preferable to construct said wind velocity
sensor, for example, by comprising a heat generating body, a
temperature sensing element which changes electric characteristics
thereof in response to a surrounding temperature, and a temperature
sensor for measuring a temperature of the cooling air, thereby said
wind velocity sensor detecting the wind velocity of the cooling air
flow on a basis of the change in the electric characteristics of
said temperature sensing element and compensating the detected
value by the temperature of the cooling air flow which is detected
by said temperature sensor. Namely, since the detection of the wind
velocity by means of said heat generating body and said temperature
sensing element receives an influence from the temperature of the
cooling gaseous body as a target to be measured, it is possible to
measure the wind velocity which is near to a true value by removing
that influence therefrom.
Further, in a case where said liquid crystal panel comprises three
liquid crystal panels for three colors of red, green and blue,
which are positioned opposing to three surfaces of a prism of a
cubic shape, respectively, it is preferable to position said wind
velocity sensor between said liquid crystal panels and said prism
so as to fully remove the affect of the air flow by said exhaust
fan.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a view of showing an embodiment of a liquid crystal
projector in accordance with the present invention;
FIG. 2 is a view of showing flow of winds within inside of the
liquid crystal projector shown in FIG. 2;
FIG. 3 is a circuit diagram of showing a construction of main
portions of a protection portion in accordance with the present
invention; and
FIG. 4 is a circuit diagram of showing the concrete embodiment of
the main portions of the protection portion in accordance with the
present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, embodiments of a liquid crystal projector according to
the present invention will be fully explained by referring to the
attached drawings.
FIG. 1 is a view of showing an embodiment of a liquid crystal
projector in accordance with the present invention; and FIG. 2 is a
view of showing flow of winds within inside of the liquid crystal
projector shown in FIG. 2.
In FIG. 1, the liquid crystal projector comprises a cooling means,
such as a suction fan 1, for sending cooling air to liquid crystal
panels, an exhaust fan 2 for exhausting the air within a cabinet 8
to outside, a light composition prism 3 for composing or combining
three colors of lights being emitted from three liquid crystal
panels, which will be explained later, a projection lens 4 for
enlarging and projecting images formed on the three liquid crystal
panels, a liquid crystal panel 5 for a red color, a liquid crystal
panel 6 for a green color, a liquid crystal panel 7 for a blue
color, and a cabinet 8, wherein a protection device 30 is provided
on an upper surface of the light composing prism 3. Further, though
not shown in the figure, a light source is provided in a space
behind the exhaust fan 2, and the light rays ejected from it are
irradiated onto the liquid crystal panels 5, 6 and 7. The light
rays emitted from the liquid crystal panels 5, 6 and 7 are composed
or combined through the prism 3 to form an image, so as to be
enlarged and projected onto a screen by means of the projection
lens 4.
The protection device 30 is formed by a print board, the main
portion of which is constructed by comprising, as shown in FIG. 3,
a main body of a wind velocity sensor 23 which is made of a heat
generating body 9 and a temperature sensitive element 10 which is
positioned in the vicinity of the heat generating body 9, a
temperature sensor 11 for measuring a surrounding temperature, and
a comparator 12 for subtracting an output of the temperature sensor
11 from an output of the temperature sensitive element 10. And, the
heat generating body 9 is heated by a constant amount of heat,
while the temperature sensitive element 10 changes electric
characteristics depending on the temperature of the heat generating
body 9, therefore, the temperature sensitive element 10 provides an
output of a detection value by detecting the substantial
temperature of the heat generating body 9. Further, the temperature
sensor 11 detects the temperature of a cooling air flowing around
the heat generating body 9. And then, the main body of the wind
velocity sensor 23 and the temperature sensor 11 are provided
projecting into a space which is formed by those liquid crystal
panels 5, 6 and 7 and the light composing prism 3. However, those
can be provided on a side surface of the protection device 30
without projecting them.
The cooling air flows which are made by the fans of the liquid
crystal projector being constructed in such manner are as shown in
FIG. 2. Namely, the air sucked by the suction fan 1 flows through a
gap between the liquid crystal panels 5, 6 and 7 and the light
composition prism 3, as well as along with outer surfaces of the
liquid crystal panels 5, 6 and 7, and hits upon a ceiling plate of
the cabinet 8 to be changed into a lateral flow, so that it is
exhausted by the exhaust fan 2 after passing inside of the cabinet
8.
An operation of the protection device 30 will be explained
hereinafter. In a case that the cooling air is supplied by the
suction fan 1 regularly, the temperature of the heat generating
body 9 decreases in relation to the wind velocity of the cooling
air. Since the decrease in the temperature of the heat generating
body 9 appears as the change in electric characteristics (for
example, a resistance value) of temperature sensitive element 10,
therefore, it is possible to detect the wind velocity by the
detection thereof. In this case, the change in the temperature of
the heat generating body 9 due to the wind velocity is effected by
the temperature of the cooling air, i.e., the surrounding
temperature. Then, in accordance with the present embodiment, the
surrounding temperature is detected by the temperature sensor 11,
with the detection value of which is compensated the detection
value of the temperature sensitive element 10 so as to detect the
wind velocity with high accuracy. The comparator 12 subtracts the
detection value of the surrounding temperature from the detection
value of the wind velocity, and if the difference is higher than a
preset reference value, it outputs a signal of abnormal heating.
Thereby, the protection device provides an instruction of turning
OFF the electric power source of a set of the projector or the
light source thereof, or it indicates a warning of the abnormal
heating.
For an instance, assuming that a piece of paper is sucked by and
stuck on the suction fan 1 and the amount of wind by suction is
reduced, the air enters into from the gap of the cabinet 8 and so
on due to sucking function by the exhaust fan 2. The air flow
around the liquid crystal panels 5, 6 and 7 are mainly of the
lateral flows of wind, therefore the air flow along with the panel
surfaces of the liquid crystal panels 5, 6 and 7 becomes very small
in the amount thereof. As a result of this, the wind velocity of
the cooling air around the heat generating body 9 is reduced, while
the temperature of the heat generating body 9 is increased. The
detection value being outputted from the temperature sensitive
element 10 rises up, then the signal of the abnormal heating is
outputted from the comparator 12.
Namely, according to the embodiment shown in FIG. 1, since the main
body 23 of the wind velocity sensor is provided at the position
just after where the cooling air by the suction fan 1 as the
cooling means passes through the liquid crystal panel portions, it
is possible to detect only the wind velocity of the air flow which
is actually effective for cooling the liquid crystal panels,
thereby protecting the liquid crystal panels with certainty. Here,
as shown in FIG. 1, it is preferable to position the upper edges of
the liquid crystal panels 5, 6 and 7 higher than the upper surface
of the light composition prism 3, thereby forming a hollow portion
being surrounded therewith, for preventing the main body 23 of the
wind velocity sensor from being exposed to the lateral wind. In the
case, if the main body 23 of the wind velocity sensor is positioned
at the side surface of the protection device 30, it is possible to
reduce the influence of the lateral wind due to the exhaust fan
2.
In FIG. 4, there is shown a concrete circuit of the construction
shown in FIG. 3. In FIG. 4, a transistor 15 corresponds to the heat
generating body 9, wherein an emitter of the transistor 15 is
connected through a resistor 16 to the electric power source, a
base thereof is connected to a juncture of resistors 13 and 14
which are connected in series between the electric power source and
ground, and a collector thereof is connected to ground. A diode 17,
corresponding to the temperature sensitive element 10, has a
cathode which is connected to ground, and an anode of which is
connected through a resistor 18 to the electric power source with
attaching to the transistor 15. A diode 20 corresponds to the
temperature sensor 11 and the same kind of the diode 17 is used for
it. The cathode of the diode 20 is connected to ground, and the
anode thereof is connected through a resistor 19 to the electric
power source, as well as to ground through resistors 21 and 22. A
comparator 12 provides an output by subtracting from a value of a
bias voltage of forward direction of the diode 17 a value at the
juncture between the resistors 21 and 22 which divide and adjust
the bias voltage of forward direction of the diode 20.
An operation of the embodiment shown in FIG. 4 will be explained
hereinafter.
An emitter current of the transistor 15 comes to be determined by
the resistors 13 and 14 and the emitter resistor 16. The transistor
15 generates the heat depending on an electric power consumption
which is determined by a product between the emitter current and
the collector-emitter voltage thereof. The bias voltage in the
forward direction of the diode 17 has a thermal coefficient of -2
mV/C.degree.. Since the diode 17 is provided attaching to the
transistor 15 which generates heat, the bias voltage of the diode
17 in the forward direction thereof changes on a basis of the
change in the temperature of the transistor 15 corresponding to the
heat generating body, thereby a voltage corresponding to this is
inputted to the comparator 12. Further, the transistor 15 is cooled
by wind blowing up vertically by the suction fan 1 as the cooling
means, the temperature of which is decreased down, and the change
in the temperature of the transistor 15 corresponds to the wind
velocity, therefore, it is possible to detect the wind velocity by
detecting the bias voltage of that transistor 17 in the forward
direction.
Further, the diode 20 can also detect, in the same manner, the
temperature of the air flow due to the suction fan 1 as the cooling
means, i.e., the surrounding temperature of the transistor 15. And,
the comparator 12 subtract the detection value of the surrounding
temperature from the detection value of the temperature of the
transistor 15 which corresponds to the wind velocity, thereby
detecting only the change of the temperature in the transistor due
to the wind velocity. If the difference between those two detection
values is larger than the reference value, it decides that the wind
velocity is small, then actuates an protection operation against
the abnormal heat generation, i.e., at least either one of the
warning indication of the abnormal heat generation or the turning
OFF of the electric power source.
In this manner, according to the embodiment shown in FIG. 4, since
the wind velocity sensor is constructed with those parts, such as
the transistor, the resistors, the diodes and the IC, etc., which
are commonly available on a market, it is possible to manufacture a
highly practical liquid crystal projector equipped with a
protection device, with a cheap price and flexibly meeting with
specifications of a set thereof.
As is fully explained in the above, in accordance with the present
invention, it is possible to provide a liquid crystal projector, in
which the wind velocity or the flow amount of the cooling air can
be measured appropriately with suppressing the effect by the air
flow due to the exhaust fan.
The present invention can be practiced in other embodiments or
forms without exceeding the sprits or main features thereof.
Accordingly, the embodiment mentioned in the above is only one
example of the present invention in all respects thereof, and it
should not be interpreted restrictedly. Breadth of the present
invention is indicated or defined by the pending claims. Further,
various modifications and/or variations belonging to the equivalent
of the pending claims are all inside of the breadth of the present
invention.
* * * * *